The annual growth of the population of prisoners within the state and federal prisons in the United States has averaged several percent per year for the last ten years. The total number of such prisoners exceeds 2 million. All felons convicted and sentenced for a crime are placed in one or another of these prisons, with little regard for the severity of the crime, whether the crime involved actual or threatened violence, or whether the crime was primarily directed against property. This approach has several disagreeable consequences. First, the federal and state governments cannot build prisons fast enough to accommodate the growing prison population, and some courts are treating prison overcrowding as a violation of the prisoners' constitutional rights. Second, the amount of fully-burdened money spent on new prisons, estimated to be $80,000-100,000 per cell, is now a substantial part of the annual budget of state and federal governments. The State of California now spends more on incarceration of prisoners than on education of University of California students. Third, prisons must be built in relatively large sizes to obtain economies of scale so that siting of such prisons is often a problem. Fourth, the average cost of providing room, board, recreation and security for a prisoner is now estimated to be about $24,000 per year, and this cost increases with inflation. Fifth, prisoners convicted of non-violent crimes are usually thrown together with, and are often preyed upon by, prisoners convicted of violent crimes. Sixth, prisoners who might still work and make a positive contribution to society are discouraged or prevented from doing so because of a lack of facilities needed for such activities.
Some workers have conceived other ways of handling some of these problems by providing portable jail or prison cells or by providing monitoring tags that must be worn by the prisoners. One early device, disclosed in U.S. Pat. No. 3,478,344, issued to Schwitzgebel et al, provides an omni-directional transceiver carried on the waist and an encoded oscillator, uniquely identifying the wearer, that communicates with the transceiver. An inmate or other supervised person in a mental institution or a prison wears this apparatus, which receives signals transmitted from a nearby central station that interrogates the wearer's unit concerning the location of the unit. The unit responds automatically. The method used for determination of location of the wearer's unit might be triangulation, which would require provision of at least three additional stations. Miller, in U.S. Pat. No. 4,495,496, discloses a-similar approach for locating miners working a in different shafts in a mine. Engira, in U.S. Pat. No. 5,153,584, discloses a similar approach for monitoring the location and status of ambulatory electrocardiogram patients in a medical facility.
Schlatter et al, in U.S. Pat. No. 3,722,152, disclose a portable jail cell that can be transported as a disassembled unit and then assembled and used within a jail or other designated security area. The cell walls and floor are made of metal and concrete, and two or more such portable cells can be placed side-by-side to conserve space. A portable cell must be placed within a jail or other secured facility to provide overall security.
In U.S. Pat. No. 4,571,904, Kessler et al disclose a patient enclosure, to be placed within and form part of a hospital room, that operates similarly to the portable cell of Schlatter et al. The patient enclosure is a separate room-within-a-room that is cleared of all furniture except the patient's bed, may include padding on the walls, and is intended to be used for patients with brain damage who must be protected from further injury by their own actions.
A location determination (LD) unit for a vehicle, relying on radiowave triangulation signals provided by an Automatic Direction Finder system, is disclosed by Wanka in U.S. Pat. No. 4,596,988. The on-board unit transmits its present location when the LD unit is interrogated by receipt of a signal broadcast by a central station, which can track the locations of several vehicles simultaneously.
Gray et al disclose a vehicle security and tracking system in U.S. Pat. No. 4,651,157. An LD unit, installed in a vehicle to be tracked, receives Loran-C signals and transmits the information in these signals, unprocessed, to a central station for determination of the vehicle's present location by triangulation. The system also monitors the values of selected parameters associated with vehicle operation and transmits an advisory signal to the central station if the value of one or more of these parameters lies outside its permitted range.
A personnel monitoring system that uses the telephone for communication between the person whose location is monitored and a central station is disclosed in U.S. Pat. No. 4,747,120, issued to Foley. The monitored person wears a bracelet and is occasionally required to take some action, such as insertion of the bracelet into a decoder that transmits a coded verification signal to the central station over a dedicated phone line that is enabled only when used. The system is provided with some means that does not allow transmission of false signals to the central station.
Watson, in U.S. Pat. No. 4,777,477, discloses a location surveillance system for a designated person, such as a parolee, that detects departure of that person from a designated site, such as an enclosed building. The person wears a sensor-transmitter, a wrist band and a current-carrying loop wrapped around the body. The sensor senses when the person leaves the building and causes the transmitter to broadcast an alarm that is received by a receiver located within the building. The system senses an attempt to remove the loop from the body, using strain gauge apparatus, and transmits another alarm signal.
U.S. Pat. No. 4,918,425, issued to Greenberg et al, discloses a monitoring system for a selected object, such as a vehicle, a person, an animal or an inanimate object. The selected object carries a transponder, with a unique identification code, that receives an interrogation signal at regular intervals, specifying its ID code, from a base station, which may be portable. The transponder then transmits a coded signal that is received by the base station, indicating that the transponder is close enough to have received and understood the interrogation signal. If the base station fails to receive the coded signal responding to its own interrogation signal within a specified time interval, the base station can cause a search to be initiated for the object, which may be a child. A similar system, which relies upon a network of stations to receive and forward the response signal to a designated base station, is disclosed in U.S. Pat. No. 5,051,741, issued to Wesby.
A house arrest monitoring system, using an identification tag that is worn near the flesh of the prisoner under house arrest, is disclosed in U.S. Pat. No. 4,918,432, issued to Pauley et al. A tag worn by a prisoner transmits a signal having a unique code portion that identifies that prisoner so that several prisoners can be sequestered at one site. A field monitoring device (FMD), connected to a telephone line, receives and analyzes these transmitted signals and determines if (1) the prisoner is present at the site and (2) the tag is being continuously worn near the flesh of the wearer. If one or the other of these conditions is not true, the FMD communicates this information to a central processing unit (CPU), using the telephone line, and personnel at this CPU respond accordingly. The intensity of the signal transmitted by the tag may be improved using a signal repeater to communicate with the FMD. One CPU is used to monitor the locations of prisoners at one or several house arrest sites. The presence of a prisoner at the site is determined primarily by receipt of a tag signal having that prisoner's code included. A prisoner, wearing a tag, could move away from the site a considerable distance before the FMD would sense this, because the location of a tag cannot be determined with much accuracy.
U.S. Pat. No. 4,952,928, issued to Carroll et al, discloses a presence monitoring and identification system, including a body condition sensor and transponder to be worn by the monitored person. In response to receipt of a radiowave request, the transponder transmits a signal to a field monitoring device (FMD), identifying the wearer and including information sensed by the body sensor, such as heart rate, skin perspiration, muscle movement, etc. The FMD is located near where the monitored person should be and periodically transmits to a central station body information on, and the location of, the monitored person. The system is intended to monitor the condition and location of a person under house arrest.
Williamson et al, in U.S. Pat. No. 4,999,613, disclose a remote confinement system in which a sequence of different, unsupervised tests are conducted on prisoners confined at a site. The tests are intended to determine the identity of a prisoner, whether a given person is present or absent at the site, and certain characteristics of the conduct of a prisoner at the site (e.g., a prisoner's sobriety). A radio transmitter, worn on the leg of each prisoner, transmits signals containing these data, which is received by an adjacent home monitoring unit, then relayed over a telephone line to a central station where these data are collected and analyzed. The present location of a prisoner cannot be accurately determined, for reasons similar to those that characterize the Pauley et al invention discussed above. U.S. Pat. No. 4,843,377, issued to Fuller et al, discloses a system that is similar to the Williamson et al patent, using breath alcohol testing and body fluid testing and verification of the prisoner identity by voice- print, graphic image matching or other means.
U.S. Pat. No. 5,052,048, issued to Heinrich for a crime deterrent system, discloses passive pursuit of a suspected perpetrator of a recent crime. Each of a plurality of citizens is provided with a short range FM or AM radio transmitter, tuned to a selected frequency for communication with a central control station. These citizens are alerted to the presence of the suspected perpetrator by a broadcast from the central station. Each such citizen that sights the suspected perpetrator transmits a report to the central station, indicating the suspected perpetrator's present location and direction of movement. The central station maps the movement of the suspected perpetrator and moves to apprehend that person.
A personnel monitoring tag with tamper detection for a person under house arrest is disclosed by Bower et al in U.S. Pat. No. 5,075,670. The tag contains a small radio transmitter that intermittently broadcasts a relatively weak signal that is received by a receiver located on the assigned site. If the arrestee leaves the site, the broadcast signal will become weaker and eventually will not be received by the receiver, in which event an alarm can be given. The tag is provided with a tamper detection circuit. The tag broadcasts a normal signal when the tag has not been tampered with and broadcasts a distinguishable tamper signal when tampering is detected. This apparatus has many interesting features, but it cannot accurately determine the location of an arrestee or detect whether the arrestee stays within a boundary defining the designated site.
A tamper indicator system including a conductive strap that is placed around a limb of a house arrestee is disclosed in U.S. Pat. No. 5,117,222, issued to McCurdy et al. When the strap is put into place, electricity is conducted through a circuit and causes a pulse counter to decrement to a selected minimum number, such as zero, over an initial strap placement period. If tampering or attempted strap removal occurs during this initial strap placement period, a transmitter notifies a monitoring person of this event.
Moore et al, in U.S. Pat. No. 5,121,096, disclose a person locator system that includes an appliance to be worn by a child or by a person with impaired senses. The appliance carries its own power supply and transmits a visual signal and an audible signal (70 dB at 2500 Hz) at selected times, such as every five seconds. The audible signal can, allegedly, be heard at 300 feet. However, this only locates the person wearing the appliance within a circle of area about 283,000 square feet, and the area covered is limited by long-term tolerance for high intensity sounds (about 85 dB). Further, this requires that a another person continuously monitor the varying level of the audible sound periodically emitted by the appliance.
Henry et al, disclose an electronic house arrest system that uses optical links and infrared communications, in U.S. Pat. No. 5,146,207. A prisoner wears apparatus that serves as transmitter and as receiver, using two concealed apertures in the apparatus. This apparatus communicates with a field monitoring device (FMD) that, in turn, communicates with a central station that receives and analyzes the data collected by the FMD. Data collected and the means of communication (telephone or modem) are similar to those disclosed in the Pauley et al patent.
In U.S. Pat. No. 5,170,426, D'Alessio et al disclose a home incarceration system that incorporates voice analysis and verification over a telephone line. The voice of a prisoner who is added to this home arrest system is initially tested to establish a voice template that subsequently can be used to verify voice communication over a phone line by that prisoner. The prisoner communicates with a central office at irregular times by phone calls, and central office apparatus verifies the location and identity of the call responder (prisoner), using the voice template and other characteristics. The location of the prisoner during the time intervals between these phone calls is not determined with this system.
An electronic house arrest system disclosed by Mitchell in U.S. Pat. No. 5,189,395 allows silent calls for assistance from a monitoring officer who makes personal and/or telephone-assisted checks of the presence and identity of prisoners at designated sites. In other respects, this system is similar to the system disclosed in the Pauley et al patent.
A telephone-based home incarceration system in which the prisoner wears a bracelet or other appliance is disclosed by Goudreau et al in U.S. Pat. No. 5,206,897. The bracelet contains an electrical circuit that has specified electrical characteristics that are monitored by an adjacent comparator circuit. If the sets of electrical characteristics do not match, indicating that the prisoner may be absent from the site of incarceration, a central station is notified by phone and appropriate action is taken. Verification of the presence and identity of the prisoner must be requested by placing a telephone call to the prisoner, who then places the bracelet in a special fixture to implement comparison of the electrical characteristics. This verification procedure probably could not be done more often than about once per hour, if the central office has many prisoners to monitor using this system.
Melton et al disclose use of a cellular interface unit for an electronic house arrest system, in U.S. Pat. No. 5,255,306. A field monitoring device (FMD) is positioned at the house arrest site and receives low power, uniquely tagged signals transmitted by a tamper-proof house arrest appliance worn by the arrestee. The FMD monitors the strength of the signals received from the appliance. When the signal strength falls below a selected threshold, the monitoring system determines that the arrestee has moved off the site, and a cellular phone network is used to alert the proper authorities at a central station. The FMD signal threshold is typically set corresponding to a separation distance of 150 feet and cannot distinguish from which direction the signals arrive.
U.S. Pat. No. 5,412,379, issued to Waraksa et al, discloses a keyless entry system, for use in automatically unlocking (or locking) a vehicle as the vehicle operator approaches (or moves away). The operator carries a portable beacon device whose beacon signal is received by a receiver in the vehicle. The beacon device includes a motion sensor that shuts down the beacon signal top conserve battery life when the beacon device is not moving.
FM subcarrier signals and AM carrier signals have been used for some types of radiowave communications. In U.S. Pat. No. 3,889,264, Fletcher discloses a vehicle location system in which the unsynchronized AM carrier signals from three or more AM radio stations form hyperbolic isophase grid lines that are used to determine location of a vehicle. The vehicle must be equipped with a three-channel, tunable receiver, and its location must be referenced to an initial known location by counting the number of isophase lines crossed after the vehicle leaves the initial location. Isophase drift is compensated for by subtraction from the count.
Dalabakis et al, in U.S. Pat. No. 4,054,880, disclose a radio navigation and vehicle location system employing three low frequency subcarrier signals received from three radio stations at a three-channel, tunable receiver located on the vehicle. Isophase lines crossed are counted after the vehicle leaves an initial known location. This system, like the Fletcher system, is a delta-position system that determines vehicle location only relative to an initially known location.
U.S. Pat. No. 4,646,290, issued to Hills, discloses use of F.C.C.-approved Subsidiary Communication Authorization (SCA) FM subcarrier signals for one way transmission. This patent discloses transmission of a plurality of messages, which may be delivered to the transmitter at a wide range of bit rates, to be transmitted at a single bit rate that is at least as large as the highest bit rate for message delivery. This method allows for downstream insertion of additional data.
An integrated radio location and communication system for a mobile station is disclosed by Martinez in U.S. Pat. No. 4,651,156. Each mobile station carries a transceiver that issues radio signals that are received by two or more signal transceiver reference sites having fixed, known locations. The transceivers at the mobile station and the reference stations are continuously phase locked to the RF carrier signal from a nearby commercial radio station. The radio station and the mobile station each transmit a brief, distinguishable range tone at a known sequence of times, and the range tone from each station is received by each reference station. From an analysis of the differences in arrival times of the range tones received from the radio station and from the mobile station, the reference stations determine the two-dimensional location of the mobile station. The mobile station uses the beat signal between two RF subcarrier frequencies to generate its range tone signal and to distinguish that mobile station transmissions from the transmissions of any other mobile station.
Young et al, in U.S. Pat. No. 4,660,193, discloses use of two SCA FM subcarrier signals, the first being amplitude modulated and the second being phase modulated, to provide a digital data transmission system. A subcarrier signal within this system may also be modulated to carry audio signals.
A multichannel FM subcarrier broadcast system that provides a sequence of relatively closely spaced channels, using independent sidebands of suppressed carriers, is disclosed by Karr et al in U.S. Pat. No. 4,782,531. The sideband signals are generated in pairs and are phase shifted before transmission. Upon receipt of the transmitted signals, the process is reversed. An earlier patent, U.S. Pat. No. 3,518,376, issued to Caymen and Walker, discloses a similar approach without use of signal phase shifting of pairs of sideband signals.
In U.S. Pat. No. 4,799,062, Sanderford et al disclose a radio location method that uses a central processing station, a plurality of signal repeater base stations with fixed, known locations, and a mobile station with a known location at any time. The central station transmits a master grid synchronization pulse, which serves as a time reference, to the other stations at a selected sequence of times. A roving station with unknown location transmits a pulse that is received by three or more base stations and is retransmitted to the central station. The central station determines the location of the roving station using the differences in time of arrival at each base station of the pulse transmitted by the roving station. The mobile station also transmits a pulse from time to time, and its known location is compared with its computed location by the central station to determine any multipath compensation required to reconcile the known and computed locations of the mobile station. The multipath compensation for a mobile station adjacent to the roving station is applied to correct the computed location of the roving station.
Ma, in U.S. Pat. No. 4,816,769, discloses receipt of SCA FM subcarrier signals for digital data paging at a radio receiver. The system measures signal-to-noise ratio of an output amplitude of a Costas loop, used to phase lock to the FM subcarrier frequency, to determine if the signal is sufficiently strong to be processed.
A system for detection of radiowave propagation time, disclosed by Ichiyoshi in U.S. Pat. No. 4,914,735, uses detection of phase differences for transmission of the signal over M (.gtoreq.2) different known signal paths to a target receiver. The transmitted signal includes a subcarrier signal, having a frequency that is higher than the transmitter clock frequency, modulated with a known modulation signal. The receiver has M demodulators for the signals received by the M different paths and has a phase comparator to compare the computed phases for each of these received signals. The phase differences are proportional to the signal path length differences, if compensation for transmission line distortions is included.
U.S. Pat. No. 5,023,934, issued to Wheeless, discloses a system for communication of graphic data using radio subcarrier frequencies. The data are broadcast on a subcarrier channel and received by a radio receiver that is connected to a computer. The computer receives the subcarrier signals, displays the graphic data on a computer screen, and performs other functions, such as transmission error checking and modification of the displayed graphic data. The system is intended for weather data communication and display.
Westfall, in U.S. Pat. No. 5,073,784, discloses a system for location of a transmitter ("unknown") at large distances, using a large network of pairs of spaced apart radiowave receivers whose locations are known and whose relative phases are synchronized. A signal, broadcast by the unknown transmitter at less than HF frequencies, is received at different time and space points by pairs of receivers. Simple geometrical computations allow determination of the location of the unknown transmitter by comparing times of arrival of the transmitted signal.
U.S. Pat. No. 5,170,487, issued to Peek, discloses use of FM sub-carrier signals for a pager system for mobile users. A plurality of transmitters are used, each of which transmits an FM subcarrier signal or a carrier signal modulated with a chosen message signal, slightly offset in time. Each page-receiving unit is assigned a time slot, during which the receiving unit dials through the set of frequencies corresponding to the FM subcarrier and modulated-carrier signals to determine if a page message has been sent for that mobile user.
A system that allows determination of an absolute location of a vehicle is disclosed by Kelley et al in U.S. Pat. No. 5,173,710. FM subcarrier signals are received from three radio stations with known locations but unknown relative phases by signal processors at the vehicle and at a fixed station with known location relative to the three radio stations. The fixed station processor determines the relative phases of the three radio stations FM subcarrier signals and broadcasts this relative phase information to the vehicle. The vehicle processor receives this relative phase data and determines its absolute location, using the phases of the FM signals it senses at its own location.
Chon, in U.S. Pat. No. 5,193,213, discloses an FM broadcast band system for receipt of relatively high frequency FM subcarrier signals. A tunable high pass receiver first circuit receives the carrier and a tunable low pass second circuit receives the subcarrier signal Each signal can then be separately processed.
A navigation and tracking system using differential Loran-C or differential Decca signalling is disclosed by Duffett-Smith in U.S. Pat. No. 5,045,861. A reference station transmits a reference signal to a mobile station and to three or more local Loran-C or Decca (fixed) stations having known locations relative to the reference station. The fixed stations retransmit the reference signal to the mobile station, where the phase received signal differences are compared to determine the location of the mobile station.
Most of these systems use a single communication system that may not work in all indoor environments or in all locations outdoors, rather than integrating two or more communication systems to provide information on the location and/or velocity of movement of a mobile user. What is needed is an integrated location determination system for automatically or discretionarily determining the present location and/or present velocity of a mobile user at a designated site, whether the user is presently outside or inside a building or other structure. Preferably, the system should include an appliance to be worn or carried by an arrestee or confinee (collectively referred to as an "monitored person" or "MP" herein) that will: (1) allow selected MPs to live on designated sites outside a conventional confinement facility for at least a portion of their confinement time; (2) detect with reasonable accuracy the present location and/or present motion of the MP at arbitrarily chosen times with time interval lengths as short as one second; (3) detect when tampering with the appliance is occurring and provide another alarm; (4) allow the MP to leave the designated site at prescribed times to seek medical attention or attend to other needs, while continuing to monitor the present location of the MP; (5) allow easy and flexible redefinition of a boundary of a designated site; and (6) provide these features with reduced use of electrical power.